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1. Field of the Invention
The present invention relates generally to an assembly for pumping liquid at constant pressure, and more specifically, to a mobile assembly for pumping liquid at constant pressure that is independent of the assembly powering engine speed.
2. Background Information
The use of a pump mounted on a mobile platform, such as a vehicle, to deliver water to fight fires is well known. Modern pumper trucks are fitted with one or more pumps that transfer water from a reservoir or fire hydrant to the fire. The pressurized pump outlet water can be directed by the fire fighters with hoses or similar devices. The water pumps on a fire truck generally are powered by the truck engine. Frequently, a hydraulic pump and hydraulic motor system is used to transfer power from the truck engine to the water pump. Some of these pumper truck systems employ a pressure governor system that changes truck engine speed to control water pump outlet pressure. Other pumper truck systems include a manual control on the hydraulic system that is adjusted to control water pump outlet pressure. These systems have some inherent drawbacks that cause problems in both operation and maintenance of the pumper truck systems. Additionally, the operation and control of two pumping systems on a truck with both systems powered by that one truck engine is most difficult.
Some examples of inventions concerned with pumps or hydraulic systems for which patents have been granted are found in the following. Miller, U.S. Pat. No. 3,785,754; Massey et al., U.S. Pat. No. 4,373,864; Swain et al., U.S. Pat. No. 4,526,516; Okazaki et al., U.S. Pat. No. 5,059,097; Marcott, U.S. Pat. No. 5,876,184; Nogaoka et al., U.S. Pat. No. 5,947,695; Houtman, U.S. Pat. No. 6,095,760; Iwanami et al., U.S. Pat. No. 6,149,401; and Mitchell, U.S. Pat. No. 6,216,456.
None of these patents provide a system for controlling a water pump outlet pressure at a specified set point that is independent of powering engine speed. Consequently, applicants have invented a system for controlling a water pump outlet pressure at a specified set point that is independent of powering engine speed, while providing many additional features that are unique to the structure described herein.
The present invention is directed to an assembly for pumping liquid at a constant, preselected outlet pressure. The assembly includes an engine connected to a variable displacement hydraulic pump driven by the engine. A fixed displacement hydraulic motor in fluid communication with, and driven by the variable displacement hydraulic pump is present. The fixed displacement hydraulic motor includes a motor speed transducer. The fixed displacement hydraulic motor drives a liquid pump with intake and outlet for liquid, with the liquid pump including a liquid outlet pressure transducer. A controller device is operatively connected to the variable displacement hydraulic pump for modulating the hydraulic output thereof. The controller device is in communication with the liquid pump outlet pressure transducer, and is in communication with the fixed displacement hydraulic motor speed transducer. The controller thereby modulates the hydraulic output of the variable displacement hydraulic pump to maintain a constant, preselected liquid pump outlet pressure that is independent of engine speed, without exceeding a preselected fixed displacement hydraulic motor speed maximum.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and detailed description that follow more particularly exemplify these embodiments.